Valves can be understood as dynamic devices that are inserted in a dynamic environment, as they have moving parts that wear out during use, packing and sealing that age and lose their effectiveness, and they are subject to vibration, ambient temperature fluctuations, pressure fluctuations, and media temperature fluctuations. Valves therefore need to be maintained, repaired, and sometimes replaced.
By João Carlos Vitorino, Director of JCV Industrial
Before delving further into the subject of maintenance and repair specifically for valves, it is necessary to understand what these services cover and how they can be divided. Both services are vital for the correct operation and good performance of valves.
Maintenance is the set of technical and administrative actions in an industrial area that aims to maintain or replace equipment or installation. Its main function is to keep the equipment in order through correct and timely interventions. The practice of maintenance provides two distinct points. The first is to anticipate the most frequent disturbances, adopting periodic maintenance to avoid unplanned downtime, generating greater efficiency. The second is that if it is not foreseen, there is a risk of interrupting all continuity of the assets and the loss can be huge.
In general, equipment maintenance consists of the set of activities necessary to increase its longevity, reducing the incidence of equipment downtime and, consequently, corrective maintenance. Maintenance is also responsible for reducing the number of repairs and thus reducing costs.
Repair, on the other hand, consists of restoring to good working order, correcting, or improving the damaged condition. Repair involves the damage or malfunction of a particular part or equipment as a whole.
Valve Specifications
Much has been discussed about the “Best Management Practices” for valves in the most varied industries. It is difficult for plant managers to consider an annual schedule of operation and maintenance for each valve in their system.
For this reason, it is important to identify the critical valves needed to keep an important area of a plant operating effectively. The maintenance and operation of these valves must be scheduled in such a way that the deadline for completion can be reached within a reasonable time.
Smaller systems must also identify critical valves within their infrastructure and schedule their operation and maintenance so that they can be performed within established time parameters to facilitate their effective availability. When establishing a valve maintenance program, the percentage of the total number of valves to be operated, maintained and/or replaced at each predetermined period must be determined.
This number or percentage should be based on the time the user has established as necessary to operate each valve.
Reactive Versus Preventive Maintenance
Reactive maintenance is commonly referred to as the type performed when a valve’s performance has already deteriorated or failed. The biggest difficulty with reactive maintenance is that it is unpredictable; you never know when it will occur. This can be even more complicated if the components needed for repair or replacement are not available at the time they are needed. Reactive maintenance is also the most expensive and least efficient.
Preventive maintenance, on the other hand, identifies the required maintenance schedule, as well as all that are impacted, to perform an efficient repair replacement. Preventive maintenance is based on trying to repair, regularize, and maintain the regular operation of the valve that is about to fail before it fails. Another aspect of preventive maintenance is to regularly maintain valves so that the ability to predict failure is better improved. Currently, the tendency to seek this improvement is through the use of monitoring software with Artificial Intelligence, which can assist in decision making and actions and consequently reduce maintenance times and costs.
One of the main problems in implementing a scheduled preventive maintenance program for valves is the scope of the task. There can be hundreds or even thousands of valves in an industrial unit. However, if a systematic maintenance schedule is applied, the task becomes simpler to perform. In general, the following operation, inspection, and maintenance rules apply: Inspections should be performed on each valve regularly and at more frequent intervals for valves deemed critical to operation. Preventative maintenance shall be performed as required or as suggested by the manufacturer and records of all operation and maintenance shall be maintained.
Valve Maintenance Environment And Procedures
Operation and maintenance procedures for various types of valves are detailed in the manufacturers’ operating manuals and in the appropriate product standards. A valve that has not been operated for several years may need to be closed using a series of up and down motions. The excess of torque to achieve positive closure can cause valve damage. Torque limiting devices are available on site and operators must follow guidelines to properly close a valve, such as applying the correct torque.
In addition, asset management requirements have allowed not only to know the location of valves in the system, but also to know their condition. Accurate and up-to-date valve records are an integral part of an industrial plant’s ability to validate the effectiveness, integrity, and reliability of its system.
The use of GIS/GPS integration in the operation of industrial plants has improved the plant manager’s ability to locate and maintain its valve infrastructure. Software has been added to help determine when valves need maintenance and/or replacement. The valve log should be detailed enough to provide information that reflects the component’s history and reliability.
Certain types of emergencies, such as explosions, make it difficult to locate or access valves on the surface, which is one reason why it is important to have the physical location of the valve, its bonnet identified as part of the record. Technology in the industry has advanced to the point where portable devices are commonly used to locate valves and report their status and update the system in real time, as is done by LDAR programs.
Repairs And Their Types
Although valve maintenance is mostly limited, repair possibilities are extensive, being limited only by economic factors. In addition to lubrication, maintenance mainly consists of correcting external fluid leakage on the stem or shaft of gate, globe, ball, and butterfly valves. In most cases, stem or shaft leakage can be stopped by tightening the packing flange and nuts, which compresses the packing and forces more against the stem.
Repairs are needed mainly when:
• Even with all possible tightening of the packing nuts, flanges or body bolting, the external leakage of the stem, shaft and body cannot be stopped.
• Opening the valve does not allow the flow to start.
• Closing the valve does not interrupt the fluid flow.
• Fluid leaks through the valve shell due to corrosion or erosion.
In-Line Repairs
The decision to do an in-line repair or send it to a repair shop depends on the nature and urgency of the repair and the ease of removal. In general, repair in a workshop is preferable to in-line repair. The extent of in-line repair is limited by the type and design of the valve and whether the line has been pressurized or drained.
In-line repairs are performed when:
• The valve is welded to the line.
• There is a lot of urgency.
• Large valve dimensions or difficult to handle.
• The valve is in a position of difficult access.
Repairs Under Pressure
Even though it is not recommended, the only inline repair that can be done, even with the line pressurized, is the replacement of the stem packing on globe and gate valves with back seats. Repacking a valve while it is pressurized is not a universally accepted procedure. Some manufacturers advise against it as they state that the back seat should only be used as a temporary measure to minimize leaks until repackaging can be done in an unpressurized condition. In addition, many technicians fear the risk of accidents and simply refuse to perform in-line repacking, particularly on valves carrying steam or other high-pressure or high-temperature fluids.
Drained System Repairs
With the piping and valves drained, many valves allow the valve bonnet cover to be removed, allowing removal of the obturator and exposing the body seating services.
Packing Replacement
Due to the possibility that the stem or shaft can be removed from the bonnet or cover, replacement of the stem packing is greatly facilitated. Whenever there is a valve disassembled for any kind of repair, it is considered good practice to replace the packing, seals and gaskets.
Replacing or Refinishing Seat Rings
For valves top-entry, the removal and replacement of seat rings is a simple accomplishment, especially if they are screwed in. However, special spanner wrenches may be required. In case of integral seating surfaces or fully welded-in seat rings, these can be refinished, still with the valve in place. It may be necessary to perform further grinding or lapping of the seat rings to get a good leak-tight fit.
Workshop Repairs
This is the most used type of repair. In a repair shop it is possible to have a control much superior to that carried out in the field, mainly in line. Due to this better control in a shop, the quality is better and the valve can be tested more effectively for body and seat tightness. Also, if the valve can be replaced with a spare, downtime of the piping system can be less than with an in-line repair and the repaired valve can become a spare.
During periodic shutdowns, it is common practice to remove all large diameter valves and send them to workshops for disassembly, inspection and, if necessary, repair. For economic reasons, small diameter piping systems, including their valves, are often scrapped and replaced rather than repaired.
Work performed in a valve shop must be controlled by a valve repair specification that defines the repairs allowed and the quality of work required.
A specification widely used by repair shops for guidance is API RP 621, which are best practices for refurbishing gate, globe and check valves and are also used as a basis for other types of valves. These specifications cover the following topics:
1. Disassembly and cleaning.
2. Inspection.
3. Evaluation of inspection results.
4. Repairs Allowed.
5. Reassembly.
6. Test.
7. Preparation for shipment.
Conclusion
Essentially, the concept of valve maintenance, which is extended to other equipment, relies on a set of actions that will promote the increase in the lifespan of the valves. Repairs, on the other hand, are more punctual actions that occur due to defects or malfunctions of the valves. Both are responsible for affecting the overall effectiveness of the equipment. In addition, a series of consequences such as loss of productivity, loss of material and long downtimes causing major financial impacts.
REFERENCES
1. The Concise Valve Handbook, Volume II: Actuation, Maintenance, and Safety Relief Michael A. Crabtree
2. Reconditioning of Metallic Gate, Globe, and Check Valves Api
Recommended Practice 621 First Edition, March 2001
3. Distribution Valves Selection, Installation, Field Testing, and Maintenance
Manual Of Water Supply Practices M44 Second Edition
4. Maintenance, Planning, Coordination and Scheduling, Second Edition
Don Nyman
Joel Levitt
Industrial Press
ABOUT THE AUTHOR
João Vitorino is Mechanical Engineer, MBA in Project Management and in Product and Services Engineering. He also has a post-grad in Industrial Valve Design Engineering. He has more than 15 years of experience in the market focused on equipment for the industrial area, mainly Oil and Gas. He is a valve consultant for Valve World Magazine and Fugitive Emissions Journal. Today he is the Director of JCV Industrial Solutions, which operates in the Brazilian market with equipment and solutions for the industry.
